The second generation of mobile communication systems represented by GSM has been ripe, and voice services have become main streams of the second generation of mobile communication systems. With rapid growth of the Internet, the demand for data communication via radio interface over-the-air has been increased significantly. However, the standard data rate for the existing GSM is 9.6 kbps/slot. Such standard data rate is not sufficient to meet the growing demand of mobile communication.
International Telecommunications Union (ITU) has been working out a standard for the third generation of mobile communication systems, which is capable of providing high speed data transmission. Since the second generation of GSM has established a large amount of fundamental networks and customers, the tendency of the development would be that both generations of mobile communication systems co-exist for a relatively long period of time. Also, to transit from the second generation to the third generation of mobile communication systems, European Telecommunications Standards Institute (ETSI) has employed developing steps according to stages based on reserving a time slot structure and a frequency band of GMS over-the-air interface. At the first stage, two operating modes, a High-Speed Circuit Switched Data (HSCSD) operating mode and a General Packet Radio Service (GPRS) operating mode, have been recommended to increase data communication capacity. At the second stage, Enhanced Data Rates for Global/GSM Evolution (hereinafter referred to as “EDGE”) has been recommended to cause a transmission rate to be three times faster by using high efficiency modulation technology, such as eight-phase shift keying (8PSK) modulation.
EDGE has been developed based on GSM. The original frequency spectrum and 200K frequency division are still being used and are compatible with the GSM. By changing a modulation method, data services up to 384 kbps can be realized. EDGE is also supported by North American IS-136 TDMA. In packet regions, EDGE and the over-the-air interface of IS-136 are completely compatible, whereby EDGE has become a global unified TDMA standard.
Digital modulation technology is one of the key technologies of over-the-air interfaces of digital mobile communication systems. Different types of digital mobile communication systems use different digital modulation technologies. Modulation methods of the existing digital mobile communication systems can be divided roughly into two types. One type is constant envelope continuous phase modulation, in which time quantization frequency modulation (TFM) and Gaussian minimum frequency shift keying (GMSK) modulation are typical. The other type is linear modulation, such as four-phase shift keying (QPSK) modulation and eight-phase shift keying (8PSK) modulation. EDGE for a transition stage developing towards the third generation of mobile communication systems uses two types of modulation modes: eight-phase shift keying (8PSK) modulation and Gaussian minimum frequency shift keying (GMSK) modulation. The parameters of the newly added eight-phase shift keying modulation in a mobile communication system have been specified in details in a protocol of the EDGE.
The eight-phase shift modulation method specified in the above protocol is not a conventional simple eight-phase shift modulation method which is only a phase modulation and cannot be used for modulation in EDGE. If the conventional simple eight-phase shift modulation method is used in EDGE, the fluctuation of the frequency spectrum will occur. In addition, because a signal may pass through an original point value, the dynamic range of a signal amplitude and the distortion of an output signal are increased, and the requirements for system devices and subsequent amplifiers become very high.
With the rapid development of very large scale integrated circuits (VLSI), it is possible to manufacture digital devices with lower cost, more functions and better performances.
A digital modulator is an essential part of a radio transmitter of a digital communication system. EDGE is a new digital communication system, wherein an eight-phase shift keying (8PSK) modulation can be used such that its digital modulator would save resources and provide easier implementation and higher signal quality. Also, the corresponding application specific integrated circuits (ASICs) can be implemented in a higher integrity wherein the consumption current is less, and the modulated signals are more precise.
Accordingly, it is desirable to provide an improved method and apparatus of 8PSK modulation.